During the procedure of a shoulder replacement operation, at least a portion of the proximal section of the humeral shaft will be replaced by a metal prosthesis. This prosthesis will generally consist of two parts: a stem that is mounted into the medullary canal of the humerus, and a head component connected in some manner to the stem. The head component replaces the bearing surfaces of the humerus and articulates with the surface of the scapula to allow the movement of the shoulder.
Modular humeral prostheses are known. The stem and head component may be supplied in “modular” form, that is, as separate connectable components. Different stem sizes and head sizes in a modular implant design provide the surgeon with some degree of inter-operative flexibility, which facilitates reconstruction of the original anatomy of the patient.
With a range of stem sizes and a range of head sizes available, the surgeon can choose a particular combination to suit the anatomy of each individual patient without having to stock a large inventory of “integral” or “unitary” humeral prostheses. As used herein, “integral” and “unitary” mean formed in one continuous piece in contrast to the separate connectable components of a modular prosthesis. For example, one patient might require a relatively small head and a relatively long stem. With a unitary prosthesis a wide range of stem lengths would be required for each head size whereas with a modular arrangement a particular head can be used with a range of stem sizes and visa versa.
Additional variations arise also as a result of individual patients requiring differing angles of inclination of the head relative to the stem and differing offsets between the axis of the head and the axis of the stem. Thus, in one patient the offset may be posterior and in another anterior.
Various shoulder prostheses are disclosed in European Patent Publication No. EP-A 0 679 375 to Odella dated Sep. 2, 1998; EP-A 0 712 617 to Walch, et al. dated Sep. 29, 1999; French Patent No. FR-A 2 664 809 to Travers dated Dec. 26, 1997; U.S. Pat. No. 3,694,820 to Scales, et al. dated Oct. 3, 1972; U.S. Pat. No. 3,803,641 to Golyakhousky dated Apr. 16, 1974; U.S. Pat No. 4,045,825 to Stroot dated Sep. 6, 1977; U.S. Pat No. 4,106,130 to Scales dated Aug. 15, 1978; U.S. Pat. No. 4,179,758 to Gristina dated Dec. 25, 1979; U.S. Pat. No. 4,865,605 to Dines, et al. dated Sep. 12, 1989; U.S. Pat. No. 4,919,670 to Dale, et al. dated Apr. 24, 1990; U.S. Pat. No. 5,358,526 to Tornier dated Oct. 25, 1994; U.S. Pat. 5,549,682 to Roy dated Aug. 27, 1996; U.S. Pat. No. 5,462,563 to Shearer, et al. dated Oct. 31, 1995 and U.S. Pat. No. 5,702,457 to Walch, et al. dated Dec. 30, 1997; and PCT International Patent Publication No. WO 96/17553 to McDaniel, et al. dated Jun. 13, 1996, which are all incorporated herein by this reference.